1. Field of the Invention (Technical Field)
The present invention relates to the field of anisotropic focusing of material streams using asymmetric tip geometries.
2. Description of Related Art
The prior art generally relates to apparatuses and methods for high-resolution, maskless deposition of liquid and liquid-particle suspensions using aerodynamic focusing. In the most commonly used embodiment, an aerosol stream is focused and deposited onto a planar or non-planar target, forming a pattern that is thermally or photochemically processed to achieve physical, optical, and/or electrical properties near that of the corresponding bulk material. The process is called M3D® (Maskless Mesoscale Material Deposition) technology, and is used to deposit aerosolized materials with linewidths that are orders of magnitude smaller than lines deposited with conventional thick film processes. Deposition is performed without the use of masks. Furthermore, the M3D® process is capable of defining lines having widths smaller than 1 micron.
The M3D® apparatus preferably uses an aerosol jet deposition head to form an annularly propagating jet composed of an outer sheath flow and an inner aerosol-laden carrier flow. In the annular aerosol jetting process, the aerosol stream enters the deposition head, preferably either directly after the aerosolization process or after passing through a heater assembly, and is directed along the axis of the device towards the deposition head orifice. The mass throughput is preferably controlled by an aerosol carrier gas mass flow controller. Inside the deposition head, the aerosol stream is preferably initially collimated by passing through a millimeter-size orifice. The emergent particle stream is then preferably combined with an annular sheath gas, which functions to eliminate clogging of the nozzle and to focus the aerosol stream. The carrier gas and the sheath gas most commonly comprise compressed air or an inert gas, where one or both may contain a modified solvent vapor content. For example, when the aerosol is formed from an aqueous solution, water vapor may be added to the carrier gas or the sheath gas to prevent droplet evaporation.
The sheath gas preferably enters through a sheath air inlet below the aerosol inlet and forms an annular flow with the aerosol stream. As with the aerosol carrier gas, the sheath gas flowrate is preferably controlled by a mass flow controller. The combined streams exit the nozzle at a high velocity (˜50 m/s) through an orifice directed at a target, and subsequently impinge upon it. This annular flow focuses the aerosol stream onto the target and allows for deposition of features with dimensions smaller than approximately 1 micron. Patterns are formed by moving the deposition head relative to the target.
Prior art related to the M3D method has disclosed apparatuses that generally use the technique of coaxial sheath flow. FIG. 1 shows the simplest geometry of concentric tubes. Innermost mist tube 10 carries the atomized material in an aerosol mist flow. Tube 10 is concentrically mounted to outer shell 12 at the proximal position 14 of assembly 16. The annular space between mist tube 10 and shell 12 forms coaxial sheath chamber 18. Sheath gas enters sheath chamber 18 at proximal location 20 such that by the time the sheath gas has traveled the length of the sheath chamber 18, the gas has established a fully developed laminar flow coaxial with the mist flow. The mist and sheath flows meet in convergence zone 22 where hydrodynamic focusing occurs. Distal cone 24 of the convergence zone 22 provides additional geometric focusing. Tip 26 may be added to assembly 16 to provide additional geometric focusing.
Liquid flow cytometry also uses hydrodynamic focusing to organize a sample flow into an extremely thin line typically to be optically analyzed. Unlike the aerosol and gas sheath M3D method, flow cytometry uses only liquid, thus benefiting from the incompressibility of liquid and laminar flow to focus sample material. The liquid sample (typically a preprocessed blood sample, analogous to the aerosol stream in the M3D® method) is focused by a liquid sheath which is typically de-ionized water or saline solution. Typically, the liquid sample is focused down to approximately a 10 micron width so that biological cells of interest are nearly aligned sequentially. From the focusing chamber, these cells directly enter an optically clear and typically square tube with an inner square chamber about 250 microns square. The square flow cell is not used to additionally focus the cells. In some cases, laser light is directed through one surface of the flow cell and an optical detector is positioned opposite the laser and one perpendicular to laser, to detect both the reflected and refracted light as the laser beam passes thru the focused sample stream. Since the sample is essentially a sequential train of cells, the changing light patterns can be analyzed and different cells can be detected and counted. Further, with special equipment the stream of cells can then be sorted and deposited into separate chambers. The construction of the focusing and optical chambers (typically called “flow cells”) are well known to the flow cytometry community and have the disadvantage of difficult alignment of the focusing chamber to the entrance of the optical chamber; with the further disadvantage of high cost. In most applications, these flow cells need to be rewashed and reused rather than thrown away. The disadvantages of reuse are obvious: cross-contamination and wasted time. Flow cytometers are also known for being relatively large in size and complexity having to pump, valve and meter various flows. When handling potentially harmful biological fluids, it can be extremely difficult and hazardous to load, unload and service these instruments.
Disposable planar liquid handling assemblies are also well known to the field of flow cytometry as is exemplified in U.S. Pat. No. 6,537,501. Rather than have many tubes and separate valves, small liquid handling cassettes are available that use many thin layers of typically plastic materials. Each layer may have different chambers of fluid paths or simply be barriers to separate one channel from another. When oriented properly and assembled, a fluidic “circuit board” is created where fluids can flow from one layer to another. With this layered approach, 2-dimensional focusing chambers have been used to focus a sample fluid into an optical chamber.